XadA-like adhesin XADA2 regulates biofilm formation in X. fastidiosa subsp. fastidiosa putatively by engaging oleic-acid derived oxylipins

BACKGROUND: The oxylipins 10-HpOME and 7,10-DiHoME derive from oleic acid and have been extensively studied for their ability to regulate contractions, microcolony formation and biofilm formation in the model organism Pseudomonas aeruginosa. METHODS AND RESULTS: Xylella fastidiosa subsp. pauca strain de Donno has been reported to produce 10-HpOME and 7,10-DiHOME in vivo when inoculated in the model plant Nicotiana tabacum or in naturally occurring infected olive trees. In this study, we deciphered the relationship among cell adhesion and oxylipins in Xylella fastidiosa subsp. fastidiosa (Temecula1 strain) and subsp. multiplex (AlmaEM3 strain). The role of the PD0744 gene, encoding for XadA2, a non-fimbrial adhesin belonging to the trimeric autotransporter family, probably involved in the surface attachment required in the initial phase of biofilm formation was investigated. PD0744 deletion mutants in two X. fastidiosa strains were generated, through homologous recombination, and the impact of its deletion on bacterial lifestyle was assessed. In vitro assays were performed to characterize the mutant phenotype, particularly in twitching motility and its capability to grow and form biofilm. Mutants showed a reduced twitching motility and biofilm formation compared to wild type strains. HPLC-MS/MS analysis revealed a decrease in 7,10-DiHOME production together with an increase of its precursor 10-HpOME in the mutants. CONCLUSIONS: 7,10-DiHOME could be a crucial signaling molecule to promote biofilm formation and twitching motility, whose synthesis likely depends on a signal transduction requiring the presence of the adhesin XadA2 and thus not working if this protein is depleted. These results help understanding the complex regulation of biofilm formation in this devastating pathogen.